The present disclosure generally relates to wind turbines, and, more particularly, to a flange section for connecting a rotor blade to a hub of a wind turbine.
Wind turbines have received increased attention as an environmentally safe and relatively inexpensive alternative energy source. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.
Generally, a wind turbine includes a rotor comprised of a hub and a plurality of blades mounted on the hub. The rotor is usually coupled to a generator through a gearbox. The generator is mounted within a housing or nacelle, which is positioned on top of a tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., thirty or more meters in diameter). Blades of such a rotor transform wind energy into a rotational torque or force that drives the generator. The rotor is supported by the tower through a bearing that includes a fixed portion coupled to a rotatable portion.
Apart from the aerodynamic design of a wind turbine rotor blade, the quality and weight of the rotor blade are essentially determined by the design of the blade root section. This blade root section connects to the rotor hub at what is referred to as the blade root joint. The blade root joint is a critical aspect of wind turbine rotor blades, as it transfers all of the aerodynamic force from the rotor blade to the remaining part of the wind turbine unit.
One difficult aspect of the design of the blade connection to the rotor hub is the load transfer from the fiber composite structure of the rotor blade to the metal structure of the rotor hub. Such a load transfer is difficult in principle due to the substantially different properties of the materials involved. Furthermore, the rotor loads are concentrated at the blade root portion, and the rotor hub and the loads exhibit a highly dynamic load spectrum.
The root section of the rotor blade is generally thicker, when compared to other blade sections, to accommodate high loads. In conventional wind turbines, the root section of the rotor blades is made of glass fiber reinforced polymers (“GFRP”) with T-bolt joints. The length of the root section of the rotor blade made of glass fiber reinforced polymers will typically be in the range of approximately 1.2 to 1.4 meters. The glass fiber reinforced polymer is generally oriented at 0 and +/−45 degrees relative to a longitudinal axis of the rotor blade in order to carry bending and shear loads. The blade root joint is typically evaluated by the fatigue life of the joint bolts.
It is expected that the electricity from clean wind resources will require more and bigger wind turbines. As the size of the rotor blade is increased, the design of the root section becomes more and more important with respect to the strength and weight of the materials used.
Accordingly, it would be desirable to provide a root section for a rotor blade that addresses at least some of the problems identified above.